The invention relates to a Thermocycler or Thermal Cycler, in particular for a polymerase chain reaction, having at least two heating devices which predetermine a temperature level for heating a specimen. One such Thermocycler is known for instance from European Patent Disclosure EP 1 252 931 A1.
Polymerase chain reaction (PCR) is a method in molecular biology that makes it possible for any arbitrary base sequence of a DNA fragment of genetic information to be duplicated many times in a simple way. In order to attain amplification factors of over 100,000, for instance, by means of multiple duplications of a base sequence, a specimen to be processed passes through a defined temperature cycle multiple times, for instance 30 times. Within the defined temperature cycle, various fixed temperature levels are kept constant for a predetermined time, while transitions between the individual temperature levels should be as short as possible.
In an apparatus known from German Patent Disclosure DE 38 08 942 A1, the temperature control is performed by placing heated liquids in succession in an incubation chamber which contains incubation cells filled with specimens. Re-circulating the liquids, however, entails considerable expenditure of time. Alternative methods use air for heating up specimen holders, containers or vessels; in that case, the lesser thermal capacity of the air in comparison to a liquid is a disadvantage, as is a lower heat transfer rate at a surface of the specimen holders. Such a method is therefore contemplated primarily for very small specimen holders.
Another conventional method for heating up specimen holders employs Peltier elements. A use of this method, too, is limited by a size of the specimen holders, since as the Peltier elements increase in size, their thermal inertia also increases. Because of this size limitation, heating by means of Peltier elements is practically unusable in methods in which a specimen holder also serves to perform other processing and analysis steps, in addition to the PCR method.
From German Patent Disclosure DE 196 46 114, a Thermocycler is known in which, by means of a structurally complicated displacement and rotation system, heating blocks are meant to be put in an alternating manner into contact with the specimens to be heated.